public class Array<E> {

    private E[] data;
    private int size;


    //构造函数，传入数据的容量capacity构造Array
    public Array(int capacity){
        data = (E[])new Object[capacity];
        size = 0;
    }

    //无参数的构造函数，默认数组的容量capacity=10
    public Array(){
        this(10);
    }

    //获取数组中的元素个数
    public int getSize(){
        return size;
    }

    //获取数组的容量
    public int getCapacity(){
        return data.length;
    }

    //返回数组是否为空
    public boolean isEmpty(){
        return size == 0;
    }

    //向所有元素后添加一个新元素
    public void addLast(E e){
        add(size, e);
    }

    //在所有元素钱添加一个新元素
    public void addFirst(E e){
        add(0, e);
    }

    //在第index个位置插入一个新元素e
    public void add(int index, E e){

        if(index < 0 || index > size)
            throw new IllegalArgumentException("Add failed. Require index < 0 || index > size. ");

        if(size == data.length)
            resize(2 * data.length);

        for (int i = size - 1 ;  i >= index ; i --)
            data [i + 1] = data [i];

        data[index] = e;
        size ++;

    }

    //获取index索引位置的原色
    public E get(int index){
        if(index < 0||index >= size)
            throw new IllegalArgumentException("index is illegal");
        return data[index];
    }

    public E getLast(){
        return get(size -1 );
    }

    public E getFirst(){
    return get(0);
    }

    //次改index索引位置的元素为e
    void set(int index, E e){
        if(index < 0||index >= size)
            throw new IllegalArgumentException("index is illegal");
        data[index] = e;
    }

    //查找数组中是否有元素e
    public boolean contains(E e){
        for(int i = 0 ; i < size ; i ++){
            if(data[i].equals(e))
                return true;
        }
        return false;
    }

    //查找宿主中元素e所在的索， 如果不存在元素e，则返回-1
    public int find(E e){
        for(int i = 0 ; i < size ; i ++){
            if(data[i].equals(e))
                return i;
        }
        return -1;
    }

    //从数组中删除index位置的元素，返回删除的元素
    public E remove(int index){
        if(index < 0||index >= size)
            throw new IllegalArgumentException("Remove failed. Index is illegal");

        E ret = data[index];
        for(int i = index + 1 ; i < size ; i ++)
            data[ i - 1 ] = data[i];
        size --;
        data[size] = null; // loitering objects

        if(size == data.length / 4 && data.length /2 != 0)
            resize(data.length/2);
        return ret;
    }

    //从数组中删除第一个元素，返回删除的元素
    public E removeFirst(){
        return remove(0);
    }

    //从数组中删除最后一个元素，返回删除的元素
    public E removeLast(){
        return remove(size-1);
    }

    //从数组中删除e
    public void removeElement(E e){
        int index = find(e);
        if(index != -1)
            remove(index);
    }

    @Override
    public String toString(){

        StringBuilder res = new StringBuilder();
        res.append(String.format("Array: size = %d, capacity = %d\n", size, data.length));
        res.append('[');
        for(int i = 0 ; i < size ; i ++) {
            res.append(data[i]);
            if (i != size - 1)
                res.append(", ");
        }
        res.append(']');
        return res.toString();
    }

    private void resize(int newCapacity){
        E[] newData = (E[])new Object[newCapacity];
        for(int i = 0; i < size ; i ++)
            newData[i] = data[i];
        data = newData;


    }
}
